The present invention relates to data storage systems, and more particularly, this invention relates to storing data on tape drives while compensating for poor performing data tracks.
In magnetic storage systems, data is read from and written onto magnetic recording media utilizing magnetic transducers commonly. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
An important and continuing goal in the data storage industry is that of increasing the density of data stored on a medium. For tape storage systems, that goal has led to increasing the track density on recording tape, and decreasing the thickness of the magnetic tape medium. However, the development of small footprint, higher performance tape drive systems has created various problems in the design of a tape head assembly for use in such systems.
In a tape drive system, magnetic tape is moved over the surface of the tape head at high speed. This movement generally entrains a film of air between the head and tape. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the magnetic tape is crucial so that the recording gaps of the transducers, which are the source of the magnetic recording flux, are in near contact with the tape to effect efficient signal transfer, and so that the read element is in near contact with the tape to provide effective coupling of the magnetic field from the tape to the read element.
Currently, data, such as a customer's data, is parsed into data sets (CQ's) of a certain size. The data set is split into 16 channels (in the case of a 16 channel drive) to be written by 16 writers to the media. As the data is being written, 16 readers in line with the writers read back the written data to confirm that the data has been written successfully. However, should a reader or writer fail or degrade, the data on that channel will not be read back or written successfully. If one channel is not written correctly, the entire data set (CQ) will not be written correctly.
As a result of this problem, the entire data set has to be rewritten in another area of the media (CQRW). Too many data set rewrites can cause the drive to lose capacity and data rate. Also, currently, tape drives have no way of compensating for a single dead track. Furthermore, in some cases, if a reader is dead, this dead reader can cause the entire drive to lose 50% of its capacity. Current products have 32 readers, and a problem with even one of these readers can cause the drive to lose almost 50% of its writing capacity. This causes the drive to be considered a failed drive and the drive would have to be replaced. Even if the track failure rate is 0.1% or 1 in 1000 tracks, this rate of track failure would lead to a 3% failure rate in drives. When tape drives and related products transition to 64 readers, this failure rate jumps to over 6%. Accordingly, a more efficient method of dealing with dead or poorly performing readers, writers, and/or tracks would be greatly beneficial.